Summary: In the mid-1980s we carried out a prospective study of early pregnancy in which we enrolled 221 health women who were planning to become pregnant. These women collected daily urine specimens for up to six months. We've assayed these specimens to describe the hormonal events of the menstrual cycle and early pregnancy. 155 women became clinically pregnant during the study, while 44 had pregnancies that ended so early that the pregnancies were detectable only by assay of urinary human chorionic gonadotropin. This unique study has been called a landmark, and continues to provide a rich resource for the description of the earliest stages of pregnancy. (More than 30,000 urine samples are still being stored.) We've published 50 papers from this study over the past two decades, some of which have led to new understanding of the fundamental processes of conception and early pregnancy. In addition, we have continued to make use of large population registries in order to pursue basic questions on pregnancy and maternal and infant health. We have worked especially closely with Norwegian colleagues in the analysis of the Norwegian Medical Birth Registry. Last year's progress: Gestational age at delivery is one of the main determinants of infant health. The statistical analysis of gestational age has become controversial due to the question of how to calculate the direct effect of preterm delivery on the infant. We provided a new insight to this problem by exposing a fundamental problem: the causes of neonatal death or illness are a mix of conditions that occur during fetal life (such as birth defects) and conditions that are important only after delivery (such as physiologic immaturity of the baby). This mix of biological conditions explains the so-called gestational age paradox, and raises an important caution to investigators who seek to understand the health effects of preterm delivery. The Chernobyl disaster in 1986 spread radiation across Europe, with some of the highest concentrations outside Ukraine occurring in Norway. We used radiation exposure data collected by the Norwegian government in combination with patient information from the national Norwegian health registries to explore any possible effects of prenatal radiation exposure on the subsequent neurodevelopment of Norwegian children,including school performance. The results were reassuringly negative. Cerebral palsy (CP) is one of the most important causes of childhood disability, with lifelong effects. We have carried out a study in Norway and Denmark, combining prenatal records with subsequent medically confirmed cerebral palsy. One of the strongest associations we have observed is between parents' education, with less-educated mothers and fathers having double the risk of having a child with CP. We plan to further explore the biological basis for this association, exploring dietary patterns and other maternal exposures that might be contributing to this increased risk.